|Monthly Tech-Tip |
3D is the cleanest material Plainsman mines in the Whitemud Formation (lowest fired speckle and low soluble salts). It is silty and has traditionally been used to cut plasticity in bodies. It is the bottom layer that we mine at Ravenscrag, SK. It is he thickest layer, we have so much of it stockpiled that it has not been extracted in the past two minings. This comes out of the ground very pure, as a silty material that weathers and breaks down readily. It is easy to process. It can readily be slurried by simply mixing the lumps into water, they slake quickly.
Recently we have discovered that, if slurried and sieved to 325 mesh, the removed particulates leave a plastic, ready-to-use porcelain for the 6-8. One that fires to steel-like strength. And fits common glazes. Even will no processing at all, just slurrying the raw lamps, it produces a stoneware that vitrifies by cone 8 and fires stable and clean across a wide range (even beyond cone 10).
Because 3D already contains natural feldspar and quartz, it is a complete material, ready-to-go for many applications. The amount of processing is the primary determiner of what it is suitable for (the more +325 mesh particles that can be remove the better it is). Industrial porcelains and stonewares for traditional ceramics (e.g. tile, brick, pottery) are made mainly from feldspar, quartz and kaolin/ball clay; each of these are available from many suppliers and each of those is often available in many grades (according to the amount of processing). These industrial minerals are selected for their physical properties (e.g. plasticity, behaviour in slurries, powder flow properties, particle size distribution) and their fired properties (e.g. whiteness, shrinkage, density, vitrification influence, chemistry). Bodies made are often less-than-optimal because of material price considerations. And sub-optimal working properties often must be tolerated to achieve a specific fired-properties goal. Plainsmamn 3D was formulated by Mother Nature. Without any addictions it already has most of what is needed for making ceramic tile, for example. Specific industrial minerals can be added in minor amounts for specific effect (e.g. 2% talc to make it matures 2 cones lower).
We are making ceramic tiles from pure 3D. It dries quickly, fits glazes well, fires strong. It's silty nature makes it unsuitable for a plastic body (e.g. for throwing). But it does have plenty of plasticity for pressing, extruding or rolling ceramic tiles. And it dries quickly with minimal shrinkage.
These bars are made for the SHAB test. The top one is cone 10 Reduction. Below that, cone 10 down to 5. The clay has been ground to 42 mesh. Notice that in reduction firing (top bar) there are almost no iron specks! And it has fired dense, to a porosity below 0.5%. At cone 10 oxidation the porosity is 0.8%. Drying shrinkage is between 5 and 5.5%. Fired shrinkage at cone 10 is less than 7%. At cone 7 it is a stoneware, having only 6% firing shrinkage and 3% porosity. This data is amazing because it is an unprocessed clay, merely ground in a hammermill to break up the lumps.
Plainsman extracts 6 different sedimentary clays from this quarry (Mel knows where the layers separate). The dried test bars on the right show them (top to bottom). The range of properties exhibited is astounding. The top-most layer is the most plastic and has the most iron concretion particles (used in our most speckled reduction bodies). The bottom one is the least plastic and most silty (the base for Ravenscrag Slip). The middle two are complete buff stonewares made by mother nature (e.g. M340 and H550). A2, the second one down, is a ball clay (similar to commercial products like OM#4, Bell). A2 is refractory and the base for Plainsman Fireclay. The second from the bottom fires the whitest and is the most refractory (it is the base for H441G).
The front tile was fired vitreous and strong at cone 01 (2050F) from a clay mined in Elkwater, Alberta (98Mix). It is fine grained and plastic, clean and low in soluble salts. The back tile is made from a silty clay from Ravenscrag, Saskatchewan (3D). It fires vitreous at cone 6 (2200F). The glaze on that tile is made using a high percentage of another clay similar to 98Mix, it melts at the higher temperature of 2200F. These tiles have dried and fired flat despite the fact they were made from plastic clay (rather than dust pressed).
Plainsman 3D! White cone 04 bodies are not vitreous and strong and neither is this. But it is plastic, smooth and fits common low fire glazes. How? 15% Nepheline Syenite (also 50% Plainsman 3D, 35% ball clay and 3% bentonite). The unmelted nepheline particles impose their higher thermal expansion on the fired ceramic. Spectrum 700 clear glaze does not craze and does not permit the entry of water (the mug is glazed across the bottom and fired on a stilt). The mug on the right is made from the same clay, it has been fired ten cones higher, cone 6! Here the nepheline is acting as a flux, producing a dense and very strong stoneware (with G2926B, GA6-B glazes). This is incredible! One note: This cannot be deflocculated and used for casting, soluble salts in the 3D gel the slurry.
Left: Plainsman 3D, a raw quarry material that fires as a dense buff stoneware at cone 6-8. Right: Plainsman Coffee clay, stained black using raw umber. Both were fired using the C6DHSC firing schedule. The inside glaze is the GA6-B Alberta Slip base.
Although not clearly visible on this photo, the unglazed body surface on both pieces has a sheen, like a glaze. And broken surfaces appear like glass, this can be seen in the broken chips on the right. Because it is angular that foot-ring is plucking all the way around. To prevent this on the other mug (left), the angle was rounded and it was fired on silica sand. This body is Plainsman 3D, wet-screened to 325 mesh with 10% feldspar. Because it is so fine-grained and contaminant-free it tolerates firing to the point of vitrification, reaching zero-porosity-density (most stonewares, and even whitewares, will blister if this is attempted). But this body does more, it can be fired cones higher and it not only resists bloating but continues to develop strength! Many potters do not realize how strong ware can be when it is fully vitrified like this. How high could this be fired? Until pieces warp during firing. These are not warping at all! If you want to make restaurant ware, knowing about super-durability is important.
Making a high quality ceramic tile
2020 testing project on the incredible clays of Southern Saskatchewn
Plainsman 3D Clay Data/Information Page